Academic IELTS Reading Practice - 32 - Sticking Power

A If Keilar Autumn, an expert in
Biomechanik at Clark College in Portland, Oregon, has his way, the first
footprints on Mars won't be human. They'll belong to a gecko. Gecko
toes have legendary sticking power - and the Clark College scientist
would like to see the next generation of Martian robots walking about on
gecko-style feet. A gecko can whiz up the smoothest wall and hang from
the ceiling by one foot, with no fear of falling.

B Autumn is one of a long line of
researchers who have puzzled over the gecko's gravity-defying footwork.
Earlier this year, he and his colleagues discovered that the gecko's
toes don't just stick, they bond to the surface beneath them. Engineers
are already trying to copy the gecko's technique - but reptilian feet
are not the only ones they are interested in.

C Some of the most persistent
'hanging' creatures are insects. They can defy not just gravity, but
gusts of wind, raindrops and a predator's attempt to prize them loose.
Recent discoveries about how they achieve this could lead to the
development of quick-release adhesives and miniature grippers, ideal for
manipulating microscopic components or holding tiny bits of tissue
together during surgery. 'There are lots of ways to make two surfaces
stick together, but there are very few which provide precise and
reversible attachment,' says Stas Gorb, a biologist in Tübingen,
Germany, working on the problem.

D Geckos and insects have both
perfected ways of doing this, and engineers and scientists would dearly
love to know how. Friction certainly plays a part in assisting
horizontal movement, but when the animal is running up a slope, climbing
vertically or travelling upside down, it needs a more powerful
adhesive. Just what that adhesive is has been hotly debated for years.
Some people suggested that insects had micro-suckers. Some reckoned they
relied on electrostatic forces. Others thought that intermolecular
forces between pad and leaf might provide a firm foothold.

E Most of the evidence suggests that
insects rely on 'wet adhesion', hanging on with the help of a thin film
of fluid on the bottom of the pad. Insects often leave tiny trails of
oily footprints. Some clearly secrete a fluid onto the 'soles' of their
feet. And they tend to lose their footing when they have their feet
cleaned or dried.

F This year, Walter Federle, an
entomologist at the University of Würzburg, showed experimentally that
an insect's sticking power depends on a thin film of liquid under its
feet. He placed an ant on a polished turntable inside the rotor of a
centrifuge, and switched it on. At slow speeds, the ant carried on
walking unperturbed. But as the scientist slowly increased the speed,
the pulling forces grew stronger and the ant stopped dead, legs spread
out and all six feet planted firmly on the ground. At higher speeds
still, the ant's feet began to slide. 'This can only be explained by the
presence of a liquid,' says Federle. 'If the ant relied on some form of
dry adhesion, its feet would pop abruptly off the surface once the pull
got too strong.'

G But the liquid isn't the whole
story. What engineers really find exciting about insect feet is the way
they make almost perfect contact with the surface beneath. 'Sticking to a
perfectly smooth surface is no big deal,' says Gorb. But in nature,
even the smoothest-looking surfaces have microscopic lumps and bumps.
For a footpad to make good contact, it must follow the contours of the
landscape beneath it. Flies, beetles and earwigs have solved the problem
with hairy footpads, with hairs that bend like the bristles of a
toothbrush to accommodate the troughs below.

H Gorb has tested dozens of species
with this sort of pad to see which had the best stick. Flies resist a
pull of three or four times their body weight - perfectly adequate for
crossing the ceiling. But beetles can do better and the champion is a
small, blue beetle with oversized yellow feet, found in the
south-eastern parts of the US.

I Tom Eisner, a chemical ecologist
at Cornell University in New York, has been fascinated by this beetle
for years. Almost 30 years ago, he suggested that the beetle clung an
tight to avoid being picked off by predators - ants in particular. When
Eisher measured the beetle's sticking power earlier this year, he found
that it can withstand pulling forces of around 80 times its own weight
for about two minutes and an astonishing 200 times its own weight for
shorter periods. 'The ants give up because the beetle holds on longer
than they can be bothered to attack it,' he says.

J Whatever liquid insects rely on,
the gecko seems able to manage without it. No one knows quite why the
gecko needs so much sticking power. 'It seems overbuilt for the job,'
says Autumn. But whatever the gecko's needs are, its skills are in
demand by humans. Autumn and his colleagues in Oregon have already
helped to create a robot that walks like a gecko. Mecho-Gecko, a robot
built by iRobot of Massachusetts, walks like a lizard - rolling its toes
down and peeling them up again. At the moment, though, it has to make
do with balls of glue to give it stick. The next step is to try to
reproduce the hairs on a gecko's toes and create a robot with the full
set of gecko skills. Then we could build robots with feet that stick
without glue, clean themselves and work just as well underwater as in
the vacuum of space, or crawling over the dusty landscape of Mars.

Questions 14-18You should spend about 20 minutes on questions 1-13, which are based on Reading Passage 32.
Look at the following statements (Questions 14-18) and the list of scientists below.

14 Some insects use their ability to stick to surfaces as a way of defending themselves.15 What makes sticky insect feet special is the fact that they can also detach themselves easily from a surface.16 Gecko feet seem to be stickier than they need to be.17 A robot with gecko-style feet would be ideal for exploring other planets.18 Evidence shows that in order to stick, insect feet have to be wet.

19 some of the practical things a gecko-style adhesive could be used for20 a description of a test involving an insect in motion21 three different theories scientists have had about how insect feet stick22 examples of remarkable gecko movements